godoc: fix bug in zip.go
godoc: fix bug in zip.go

The result of sort.Search is in the interval [0,n);
specifically, if no entry is found, the result is n
and not -1.

R=dsymonds
CC=golang-dev
http://codereview.appspot.com/4982041

apparentlymart/golang,apparentlymart/golang,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,dsriram/golang,gnanderson/go,dsriram/golang,dsriram/golang,gnanderson/go,tv42/old-go,gnanderson/go,gnanderson/go,apparentlymart/golang,dsriram/golang,dsriram/golang,apparentlymart/golang,tv42/old-go,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang